In a vehicle, it may be of interest to determine the presence and/or position of a living being in an interior of the vehicle. This may e.g. be used when paying fees or tickets for the vehicle, wherein the costs depend on the number of persons in the vehicle. On some roads, there may be a special lane for vehicles comprising at least two persons. The information regarding presence of the persons may then be used to check that the vehicle fulfils a requirement for a minimum number of persons. Further, the information about the position of the living being may be used in safety systems of the vehicle, e.g. a safety arrangement may only be applied if there is a person in the seat. Other safety arrangements may only be applied if that person is correctly positioned in relation to the safety arrangement, e.g. the person is not leaning forward.
Document EP 2 472 289 B1 discloses a device and method for levying vehicle tolls depending on the number of passengers in a vehicle. The system uses a Doppler radar or UWB-IR, ultra-wideband impulse radar. The radar signal is used to determine heart beating or breathing of the passengers. A first embodiment discloses the use of one radar unit. Information about the different passengers is provided by signal analysis of the reflected radar signal, wherein different signal patterns are associated with the different persons. In a second embodiment, there is one radar unit directed towards each seat, such that the presence or non-presence of a passenger in each seat may be determined.
The first embodiment of EP 2 472 289 B1 determines the number of passengers, but not their positions. The second embodiment of EP 2 472 289 B1 determines the presence or non-presence of a living being for each one of a plurality of vehicle seats. However, one radar unit is utilized for each seat, i.e. for a vehicle with five seats, five radar units are utilized and for vehicle with seven seats, seven radar units are utilized, etc.